Replacing Roof, So many questions, 1st off, sarking boards.?

[Carlos74]

Hey All,

Firstly just wanna say thanks to all who input. Have been reading this forum for a while, some great threads and have learn't a lot.

Anyway's back to my question. I've started getting quotes in on replacing our roof. Semi detached victorian with plain tiles. It's a bit tired looking and I've started to have a few leak's here and their. I'm still undecided on the replacement covering but will either be similar plain tiles again or slates, this may effect my question, I don't know.

Now the 2 different roofers I've had round look at my roof have given different answers on if to remove the sarking boards or not? See pic, one has said leave them on and cross batten, other has said to remove? Now I understand they bring strength to the roof but also extra weight?

Anyone have any preferences, pro's and cons about these boards?

Any help would be great.

Thanks in advance,


C
ps. I also have some other questions as I have 2 attic rooms I want to insulate while the roof is getting done, but I'll save that until I have some better pics to bring on here.

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[Alastairreid]

No need to remove the sarkin boards, counter battens would be fitted before the tile battens to create an airflow.

 

[Carlos74]

Hi Alistair,

Thanks for the reply.

Ok, that kinda leads me to my next question if the boards stay and aren't a problem.

The picture is from one of the hidden eaves in the roof 'the back', I have 2 rooms up in the roof I want to insulate and use. At the moment the rooms walls are made out of hardboard out onto those rafters and uprights holding the purlin's. So not very warm or decoratively nice, wood chipped. We only use the rooms for storage at the moment but want to start using as bedroom's so need to get them updated and decorated. I'm planning to remove the hardboard & insulate the rooms to a high standard cheaply. Plan was going to use insulation boards between the rafters then re-plasterboard.

However, I realise the rafters aren't that deep so limited on the thickness I can use with insulation. Also, as you mentioned we would have airflow between the felt and board with counter battens. Would I still need to leave a 50mm gap between the insulation boards and the sarking boards for airflow as I've been told form inside. Or could I push the the insulation flush against the sarking boards? I'm assuming not.

If thats the case and the 50mm gap needs to exist, this leaves me with limited insulation depths I can use. Wondered if I could use cosyboard, insulation backed plasterboard or could I add wood to the rafters or something to give me better depth?

Hope this make's sense & thanks again.

C

 

[Alastairreid]

You would have to increase the depth of the rafters by strapping the underside, the insulation will need a 50mm airgap maintained above as well as high and low level ventilation.

You will need a vapour barrier between the plasterboard and insulation as well as an insulation layer beneath and over the rafters.

 

[noseall]

Seems to me Carlos that you are getting yourself into something that requires a bit more thought.

You may need a design spec' for your insulation needs and this may have consequences in how you go about doing your re-roof. These jobs whilst seem simple can be complex building regulations affairs.

 

[Carlos74]

Thanks Alistair, not the answers I was looking for but thanks nevertheless . It's never easy is it

Yes noseall, doe's seem to be a little more complex than banging up some insulation. The strapping sounds like it'll add weight to the roof, maybe a reason to remove the boards?

Agree, want to have a plan on the insulation before hitting the button on the re-roof. Hmm, so maybe I go for a skinnier insulation, anything out their that will get to the below thermal propertys off bromley council site.

2. Pitch roof with insulation at ceiling level - 0.16 W/m²K

I suppose I need to measure the rafters tonight. Anyone have any idea's on any other options other than strapping. Could I as mentioned cosyboard striaight onto the rafters?

Thanks again,

Carl
ps. Am sure the sarking boards add some thermal quaility's, so a positive to keep. Although useless to reg's as can't be measured.

 

[Carlos74]

Ok so I have 4 x 2's for rafters.

Looking into the insulation tonight online, the insulation inbetween rafters and under systems to produce .16 u value. I'm looking at 750mm for each roughly to get that kind of U value, + the 50mm gap. So roughly need to add another 4 x 2 on the rafters. Wow, does that really sound correct?

Just to confirm from the reg's angle. These rooms have always been up in the roof space and always labelled as bedrooms, so not a loft conversion or changing the space. They don't and have never had insulation on the pitch's.

But as I'm adding insulation and this isn't a new development. Do I need to comply on the thermal requirement side of things.

 

[noseall]

But as I'm adding insulation and this isn't a new development. Do I need to comply on the thermal requirement side of things.

Probably.
Building Regulations parts B, P and L will likely apply.

 

[Carlos74]

Ok so I need to insulate and I need to meet regs. Any comments on this kingspan solution that fully fills the rafters. Could I go unventilated?

View media item 89847

 

[Alastairreid]

Never seen that detail before!

well if thats what kingspan say cant really argue.

Building control may see it different.

 

[Carlos74]

Think I'll avoid and keep ventilated.

Had another roofer come and view the weekend. He's saying remove the boards. If we leave the boards on the roof will raise, maybe a problem so best to remove them. He'd use a breathable felt then baten then tile etc.

He also suggested he could push the insulation in from outside inbetween the rafters while replacing the roof. Would make life easier for me if I could meet .19 U regs with 50mm insulation. Hmmmm.

 

[Carlos74]

Sorry all, doe's anyone else have a view on sarking boards?

Are they just one of those things and preference to the roofer to keep or remove? The first roofer mentioned skip costs to remove & the time, the second said 'get'em gone'.

 

[Alastairreid]

Before removing the boards you should check they are not part of any bracing elements of the roof.

 

[Carlos74]

Alistair, thanks for the heads up. We do have a loft space above the attic rooms, haven't inspected that closely but will do ref these boards and the structure side of things up there.

Just to go back a step. In your opinion, is it just a personal preference about retaining these boards if they don't do any bracing. Just want to double check there's no gotcha's if they stay or go.

Going to try and talk to bromley building control ref keeping these boards & insulation. If I retain the boards and have an airflow top side between the felt and boards. Do I still have to maintain as well a 50mm airflow underneath the sarking boards and insulation. Could I put some vented tiles in the loft area above the attic rooms to increase airflow up these.

Whats the chance's building control will talk to me,hmmm.

 

[Alastairreid]

Local authority building control are normally very helpful in my experience.

Sarking boards were always used up here in Scotland due to more extremes of weather. It wasnt until recently they started constructing roofs without the sarking (engineered trusses).

Personally i would retain them...why would they have used sarking in the first place.

The airflow is supposed to be between the underside of the sarking and top of insulation..both high and low level.